Thin disk laser with large numerical aperture pumping

ABSTRACT

An optical system has a high power diode pump source and a thin disk gain media. An optical coupler is positioned between the diode pump source and the thin disk gain media. The optical coupler produces a beam with a large numerical aperture incident on the thin disk gain media.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to U.S. patent application Ser. No.______ not yet assigned, identified as Attorney Docket No. 18120-0011,and U.S. patent application Ser. No. ______ not yet assigned, identifiedas Attorney Docket No. 18120-0012, both of which are filed concurrentlyherewith.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a thin disk gain media for lasers andamplifiers, and more particularly to an optical system for pumping thegain media with a large numerical aperture beam.

[0004] 2. Description of Related Art

[0005] As diode lasers and diode laser arrays have become more powerful,higher power diode-pumped solid-state lasers have become possible. Manyschemes have been proposed to efficiently couple the pump light frommultiple high power diode bars or diode bar arrays into the solid-stategain medium. It is desirable to build a high power laser that alsopossesses a good mode quality, and this is a challenge as the power ofthe laser increases. One scheme that achieves both high power and goodmode quality is the thin disk laser configuration described in U.S. Pat.No. 5,553,088 by Brauch, Giesen, Voss and Wittig and in Optics Lettersvolume 20, page 713 (1995).

[0006] In the thin disk configuration, the gain medium is typically adisk of a few millimeters in diameter and only a few hundred micronsthick. It is attached to a heat sink on the cooling surface. That samecooling surface is coated to reflect both the pump light and the laserlight. Thus the thin disk laser is an end-pumped design with the pumplight and the laser light being collinear. If the pump mode and thelaser mode are matched in size, then the mode quality can be quite goodwithout any loss in efficiency. This is typical of end-pumped designsand is in contrast to side-pumped configurations. If the disk is thinenough, the cooling will be 1-dimensional and the thermal gradient willalso be collinear with the laser beam. Thus, the thermal lensing acrossthe beam will be quite small. This is in contrast to most otherend-pumped designs where the thermal lensing is significant and must bepartially compensated by the design of the laser cavity.

[0007] The thin disk design does have added complexity however, becausethe pump light must be passed through the gain medium multiple times.The paper “pumping schemes for multi-kW thin disk lasers” by Erhard,Karszewski, Stewen, Giesen, Contag and Voss in Proceedings of AdvancedSolid State Lasers conference 2000, OSA Trends in Optics and PhotonicsSeries, Volume 34, page 78 teaches that: “for quasi-three-level systemslike Yb:YAG also the reabsorption of the laser wavelength in the laseractive medium plays an important role. Increasing the pump absorption inan end-pumped configuration by increasing the length of the laser activemedium also increases the reabsorption losses for the laser wavelength.

[0008] Therefore the total efficiency is limited in such aconfiguration. The way to higher efficiency is the reduction of thereabsorption losses by reducing the length of the crystal and/or byreducing the doping concentration while simultaneously keeping theabsorption of the pump radiation high. In an end-pumped configurationthis can be achieved only by multiple passing of the pump radiationthrough the medium as it is demonstrated in the thin disk design.” Theauthors continue by showing that increasing the number of passes thepump light makes through the medium leads to higher efficiency whenthinner crystals are used.

[0009] There are secondary reasons for the multiple passes of the pumplight. The disks must be kept thin in order to preserve the1-dimensional cooling. In addition, the fracture limit scales as theinverse of the thickness of the disk. Unfortunately the maximum dopinglevel, and thus the maximum absorption, for most gain medium is limited.One of the gain media with the strongest absorption is Nd:YVO₄(Vanadate). Vanadate is a 4 level laser and thus complete absorption ofthe pump is optimal. Using Vanadate with a doping of 1 at. %, fourpasses of the pump radiation and a 400 micron thick disk are required toabsorb 86% of the pump radiation. Higher Nd doping levels in Vanadateare possible, but lead to a reduced lifetime and reduced efficiency.

[0010] Recent work has focused on designs for achieving a large numberof passes for the pump light. In designs utilizing 16 passes of the pumplight, the light from the diode bars is typically fiber coupled into afiber bundle with a numerical aperture (NA) of 0.1. This pump light isimaged by a mirror onto the disk. The remaining pump light is collectedby another mirror and imaged back to the disk. A series of 8 mirrors isthen used to create the 16 passes of the pump light through the gainmedia. Each of the mirrors needs to be large enough to capture the pumpbeam with a numerical aperture of 0.1.

[0011] In an alternative design, a large parabolic mirror is used and 8different segments of this mirror replace the 8 separate mirrors of theprevious design. Each segment of the parabolic mirror must now have anNA of 0.1. This requires either a brighter pump source (NA<0.1) or alarger high NA parabolic mirror. A brighter pump source can produce thesame spot size with a lower NA or alternatively a smaller spot size witha constant NA.

[0012] Recently two stoichiometric materials that incorporate Yb in thecrystal matrix have been demonstrated. The first, YbAG, is the hostcrystal YAG with all of the Yttrium replaced by Ytterbium. This crystalis thus Yb:YAG with 100% Yb doping. It is described in “Laserdemonstration of YbAG and Materials properties of highly doped Yb:YAG”by Patel, Honea, Speth, Payne, Hutcheson and Equall in IEEE Journal ofQuantum Electronics, vol. 37, page 135 (2001). In YbAG it has beendemonstrated that 100% doping of the YAG with Yb can still lead to agood laser crystal without significant degradation in the lifetime. Mostimportantly, all of the pump light can be absorbed in a disk of lessthan 300 microns with just a single pass.

[0013] A second stoichiometric crystal called KYbW is based on the hostKYW with all of the Yttrium again replaced by Ytterbium. It is describedin “Laser operation of the new stoichiometric crystal KYb(WO₄)₂”, byKlopp et al., in Applied Physics B, vol.74, page185 (2002). Thecalculated absorption length in KYbW is less than 20 microns.

[0014] These highly doped stoichiometric materials present several newpossibilities. One is to continue to use multiple passes of the pumplight and thinner disks. This will improve the cooling. The otherpossibility is to design simpler and less expensive systems. Higher NApump schemes have not previously been contemplated for thin disk systemsbecause of the challenges of using high NA mirrors with multiple passpumping. High NA pump schemes have several advantages, however,especially with respect to reducing complexity and cost.

[0015] A first advantage of higher NA pump schemes is that less brightpump sources can be used. Higher NA pump schemes make sense with thindisk gain media, because the pump beam does not diverge within the gainmedia. These less bright pump sources can include diode stacks and diodearrays with fewer beam shaping optics. Typical beam shaping opticsinclude fast axis collimating lenses on each diode bar, beam shapersthat transform the beam quality in the horizontal and verticaldirections to symmetrize the pump beam, and polarizing optics that allowtwo diode stacks of opposite polarization to be combined. Each of thesebeam shaping optics help preserve the brightness of the pump source, butincrease the cost and complexity of the pump source.

[0016] Second, non-imaging concentrators can be used in place of imagingsystems. Lens ducts or hollow funnel concentrators can be utilized.These non-imaging concentrators convert a large beam with a low NA froma diode stack into a smaller beam with a larger NA. This allows a largediode stack, typically 1 cm square, with space between the diode barsfor efficient cooling, to be used. The concentrator can reduce the beamsize by a factor of 4 or 5 but the NA of the beam will increase by thesame factor. A hollow funnel is the preferred embodiment when relayingthe pump beam to the gain media with a minimum cost is required.

[0017] Third, multiple pump sources can be incident on the thin diskgain media from different angles. Thus individual diode bars can beaimed at the pump spot on the gain media from multiple directions.Removing the heat from these separate bars is then made easier. Multiplediode stacks displaced around the disk can be used as well to increasethe power. Each diode stack has its own coupler and would deliver thepump beam to the disk from a different direction.

[0018] There is a need for an improved optical system, and its methodsof use, that has a thin disk gain media. There is a further need for anoptical system, and its methods of use, that has a diode-pumped thindisk gain media and utilizes a high NA pumping scheme to reduce the costand complexity.

SUMMARY OF THE INVENTION

[0019] Accordingly, an object of the present invention is to provide adiode-pumped laser, and its methods of use, with high power and a goodmode.

[0020] A further object of the present invention is to provide adiode-pumped laser, and its methods of use, with high power and a goodmode, that is simpler and less expensive.

[0021] Accordingly, these and other objects of the present invention areachieved in an optical system that has a high power diode pump sourceand a thin disk gain media. An optical coupler is positioned between thediode pump source and the thin disk gain media. The optical couplerproduces a beam with a large numerical aperture incident on the thindisk gain media.

[0022] In another embodiment of the present invention, an optical systemis provided that has at least first and second high power diode pumpsources which produce first and second pump beams. A thin disk gainmedia is provided. An optical coupler is positioned between each of thediode pump sources and the thin disk gain media. The first and secondpump beams are incident on the thin disk gain media from differentdirections.

[0023] In another embodiment of the present invention, a method ofpumping a thin disk gain media produces a high power diode pump beamfrom a pump source. The high power diode pump beam is passed through anoptical coupler positioned between the diode pump source and a thin diskgain media. A high numerical aperture output beam is produced from theoptical coupler. The high numerical aperture output beam is incident atan incidence surface of the thin disk gain media.

[0024] In another embodiment of the present invention, a method isprovided for materials processing, including but not limited tomicro-machining, rapid prototyping, annealing, ablation, initiatingchemical processes, medical applications and the like, that produces ahigh power diode pump beam from a pump source. The high power diode pumpbeam is passed through an optical coupler positioned between the diodepump source and a thin disk gain media. A high numerical aperture outputbeam is created from the optical coupler. The high numerical apertureoutput beam is incident at the incidence surface of the thin disk gainmedia to produce an output beam. The output beam is directed to anarticle to be processed.

[0025] In another embodiment of the present invention, a method ofpumping a thin disk gain media is provided. First and second pump beamsare produced from first and second pump sources. The first and secondpump beams are each passed through an optical coupler positioned betweenthe diode pump source and a thin disk gain media to produce first andsecond gain media beams. The first and second gain media beams areincident on the thin disk gain media from different directions.

BRIEF DESCRIPTION OF THE FIGURES

[0026]FIG. 1 is a schematic diagram illustrating one embodiment of anoptical system of the present invention that includes a diode pumpsource, a coupler, a thin disk gain media and a heat sink.

[0027]FIG. 2 is a schematic diagram illustrating an embodiment of anoptical system of the present invention that includes two diode pumpsources, each with a coupler and the thin disk gain media.

[0028]FIG. 3 is a schematic diagram of an embodiment of the presentinvention with a diode pump source, a coupler and a thin disk gain mediawhere pump light passes through the thin disk gain media four timesusing a single mirror to redirect the pump light back to the thin diskgain media.

[0029]FIG. 4 displays the calculated reflectivity of an anti-reflectioncoating as a function of wavelength and angle.

[0030]FIG. 5 displays the calculated reflectivity of a high-reflectioncoating as a function of wavelength and angle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Referring to FIG. 1, one embodiment of the present invention isan optical system 10 with a high power diode pump source 12 and a thindisk gain media 14. One example of a thin disk gain media is disclosedin U.S. Pat. No. 5,553,088, incorporated herein by reference. An opticalcoupler 16 is positioned between the diode pump source 12 and the thindisk gain media 14. Suitable distances between diode pump source 12 andthin disk gain media 14 are in the range of 10 to 200 cm, not includingthe length of an associated fiber, if any. Optical coupler 16 produces abeam 18 that has a large numerical aperture incident on thin disk gainmedia 14.

[0032] Pump source 12 can be one or more diode bars, a linear array ofdiode bars or, preferably a vertical stack of diode bars and can have apower of at least 50W, and more preferably at least 200W.

[0033] In various embodiments, the numerical aperture of beam 18incident on thin disk gain media 14 is greater than 0.35, greater than0.4, greater than 0.5 and the like.

[0034] Optical coupler 16 can be a non-imaging concentrator includingbut not limited to a lens duct, a hollow funnel concentrator, and thelike. One example of a suitable funnel concentrator is disclosed in U.S.Ser. No. 09/401,146, filed Sep. 22, 1999, incorporated herein byreference. Further, optical coupler 16 can be a cylindrical lens tocollimate a fast axis divergence of the pump source 12, a combination ofseveral cylindrical lenses, and the like. Optical coupler 16 may alsocontain a beam shaper, a polarization beam combiner, a wavelength beamcombiner, a beam homogenizer and the like. The beam shaper transformsthe quality of beam 18 in the horizontal and vertical directions inorder to symmetrize the beam 18. The beam shaper can be made from anarray of micro-mirrors, a stack of plates or a pair of mirrors asdisclosed in U.S. Pat. No. 5,825,551, incorporated herein by reference.In one embodiment, optical coupler 16 converts a large beam that has alow numerical aperture which can be 0.1 from the diode pump source 12into a smaller beam with a larger numerical aperture which can be 0.2 to0.5.

[0035] Further, optical coupler 16 can be selected that reduces a beamsize from the diode pump source 12 by a factor of at least two and morepreferably 3 or 4. The numerical aperture of the beam from the diodepump source 12 then increases by a factor of at least two and morepreferably 3 or 4.

[0036] Thin disk gain media 14 can be in a variety of different shapesincluding but not limited to a thin round plate or a thin square plate.Thin disk gain media 14 has an incidence surface 22 and a coolingsurface 24. Incidence surface 22 is the surface through which beam 18 isincident on, and cooling surface 24 is the surface through which theheat is removed. Incidence surface 22 and cooling surface 24 aretypically the opposite sides of the thin disk gain media 14, but theycan be the same surface if a transparent heat sink material such asundoped YAG is used. Thin disk gain media 14 can have dimensions wherethe thickness is much smaller than the aperture. Examples of suitablesizes include but are not limited to a aperture of 2 to 50 mm, and athickness of 10 to 500 microns.

[0037] Bonding material 26, including but not limited to a solderingmaterial, a glue and the like, couples cooling device 28 to coolingsurface 24. Suitable cooling devices 28 include but are not limited to aheat sink made of metal, beryllium oxide, undoped YAG, ceramic materialsand the like.

[0038] Thin disk gain media 14 can be made of a variety of differentmaterials including but not limited to Yb:YAG, Yb:KGW, Yb:KYW, Yb:S-FAP,Nd:YAG, Nd:KGW, Nd:KYW, or Nd:YVO₄. Thin disk gain media 14 can also bemade of a semiconductor material. To obtain a high absorption in thindisk gain media 14, a stoichiometric gain material such as thosedescribed herein can be utilized. By way of example, and withoutlimitation, the stoichiometric gain material can be a stoichiometricYb³⁺ material, such as YbAG, KYbW and the like.

[0039] Referring now to FIG. 2, one embodiment of the present inventionis an optical system 110 with at least first and second high power diodepump sources 112 and 114 which produce first and second pump beams 116and 118. A thin disk gain media 120 is provided. An optical coupler 122is positioned between each of the diode pump sources 112 and 114 andthin disk gain media 120. First and second pump beams 116 and 118 areincident on thin disk gain media 120 from different directions.

[0040] Referring now to FIG. 3, another embodiment of the presentinvention is an optical system 210 with a high power diode pump source212 and a thin disk gain media 214. An optical coupler 216 is positionedbetween the diode pump source 212 and thin disk gain media 214. Opticalcoupler 216 produces a beam 218 that has a large numerical apertureincident on thin disk gain media 214. Beam 218 makes two passes throughthin disk gain media 214 and the unabsorbed pump light is directed backto thin disk gain media 214 by optical coupler 220 and a single mirror230. Beam 218 then makes a third and fourth pass through the gain media.

[0041] Coatings can be fabricated that are suitable for the largenumerical aperture of the pump beam, according to the invention. Suchcoatings can be suitable for both the pump radiation from the diodes andthe laser radiation emitted by the optical system.

[0042] An anti-reflection coating on the incident surface of the gainmedia can consist of a single layer of magnesium fluoride. It can alsoconsist of multiple dielectric layers. FIG. 4(a) shows the calculatedreflectance of 7 alternating dielectric layers of SiO₂ and Ta₂O₅designed to suppress reflection off the incident surface of a thin diskgain media with a refractive index of about 2, as a function ofwavelength at normal incidence. Such a coating can be suitable for KYbWand other similar gain media. The reflectance stays well below 0.1% fora wavelength range from 1000 nm to above 1100 nm, which can allow forbroad wavelength tunability of the optical system, and which also cansupport the broad wavelength spectra needed to form a femtosecond pulse.

[0043]FIG. 4(b) shows the reflectance of the same coating as a functionof incidence angle with respect to the surface normal of the thin diskgain media for unpolarized light at a fixed pump wavelength of 940 nm.The reflectance stays below 4% over a range of incidence angles of up to60 degrees with respect to the surface normal, and below 10% for anglesup to 70 degrees. The reflectance curves for other pump wavelengthsbetween 930 nm and 950 nm are very similar for this coating. A pump beamincident from cone angles between +70 and −70 degrees corresponds to anumerical aperture of sin((70°−(−70°))/2)=0.94. A pump beam incidentfrom cone angles between +10 and +70 degrees corresponds to a numericalaperture of sin((70°−10°)/2)=0.5.

[0044] It can also be beneficial to couple a thicker media to the top ofthin disk gain media 14, 120 and 214. For example, a thin disk of highlydoped Yb:YAG or YbAG can be diffusion bonded to undoped YAG that istransparent for the emission 18, 116, 118 and 218 of the pump diodes. Inthis case the anti-reflection coating can be deposited on the incidentsurface of the thicker media.

[0045] A high-reflectance coating on the reflecting surface of thin diskgain media 14, 120 and 214 can also consist of multiple dielectriclayers. It can also include other materials such as metals like copper,silver, gold, and the like. In one embodiment, the high reflectancecoating can be applied to the back side of thin disk gain media 14, 120and 214, i.e. the surface opposing the incident surface. FIG. 5(a) showsthe calculated reflectance of a suitable high-reflection coating for again material with a refractive index of about 2 as a function ofwavelength at normal incidence. This design consists of 20 alternatingdielectric layers of SiO₂ and Ta₂O₅ and a copper layer. Such a coatingcan again be suitable for KYbW and other similar gain media. Thereflectance stays well above 99.98% for a wavelength range from below1000 nm to about 1100 nm, which can allow for broad wavelengthtunability of the optical system, and which also can support the broadwavelength spectra needed to form a femtosecond pulse.

[0046]FIG. 5(b) shows the reflectance of the same coating as a functionof incidence angle measured outside thin disk gain media 14, 120 and 214with respect to the surface normal of the thin disk gain media 14, 120and 214 for unpolarized light at a fixed pump wavelength of 940 nm. Thereflectance stays close to 100% over a range of incidence angles of upto 25 degrees with respect to the surface normal. For larger angles, upto 60 degrees, the reflectance drops but on average still stays above90%. For angles larger than 60 degrees the reflection is again close to100%. The reflectance curves for other pump wavelengths between 930 nmand 950 nm are also very similar for this coating.

[0047] When optical systems 10, 110 and 210 are configured as lasersystems, the laser beams can be mode matched to the gain region in thethin disk gain media 14, 120 and 214. This allows the generation of agood output mode without sacrificing efficiency. Due to theone-dimensional cooling, the thermal gradient is also collinear to thelaser beam and thus the thermal lensing is small.

[0048] When optical systems 10, 110 and 210 are configured asdiode-pumped laser systems, they are useful for a variety of differentapplications. By way of illustration, and without limitation, a Yb dopedgain media is useful for constructing mode-locked laser sources. Diodepumped lasers 10, 110 and 210 can produce subpicosecond pulse durationsthat can be obtained using semiconductor saturable absorbers as themode-locking devices. High-power subpicosecond diode pumped lasersystems 10, 110 and 210 can also be used to synchronously pump an OPOand produce a tunable source of subpicosecond pulses. A temperaturetuned LBO crystal can be used as the parametric gain media for the OPO.Additionally, diode pumped lasers 10, 110 and 210 can be utilized inpolarization coupled mode-locking systems.

[0049] Optical systems 10, 110 and 210 can be utilized as amplifiers.They can be configured as the gain element in either a multi-passamplifier or alternatively, a regenerative amplifier. A regenerativeamplifier system for amplifying pulses from a mode-locked oscillator iscapable of generating subpicosecond pulses with energies of 1 mJ. Suchamplifier systems can be based on chirped pulse amplification and usegrating pairs for stretching the pulse prior to amplification andcompressing the pulse after amplification. By way of example, andwithout limitation, diode-pumped systems 10, 110 and 210 can be sourcesof high peak power, subpicosecond pulses that are suitable formicromachining applications where high precision machining or reductionof thermal damage are important.

[0050] Further, diode-pumped systems 10, 110 and 210 can be intra-cavityfrequency doubled lasers with a good spatial mode. Non-critically phasematched LBO can be used as the frequency doubling crystal to produce ahigh power source of green light with as much as 20 to 50 W of power formany applications including pumping other lasers. A single frequencysource of either infrared, or green light, can be achieved because ofspatial hole burning in thin disk gain media 14, 120 and 214, and findsapplications in pumping both other lasers and single frequency OPOs, aswell as spectroscopy and metrology.

[0051] The foregoing description of a preferred embodiment of theinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in this art. Itis intended that the scope of the invention be defined by the followingclaims and their equivalents.

What is claimed is:
 1. An optical system, comprising: a high power diodepump source; a thin disk gain media; and an optical coupler positionedbetween the diode pump source and the thin disk gain media, the opticalcoupler producing a beam with a large numerical aperture incident on thethin disk gain media.
 2. The system of claim 1, wherein the pump sourcehas a power of at least 50W.
 3. The system of claim 1, wherein the pumpsource has a power of at least 200W.
 4. The system of claim 1, whereinthe numerical aperture of the beam incident on the thin disk gain mediais greater than 0.35.
 5. The system of claim 1, wherein the numericalaperture of the beam incident on the thin disk gain media is greaterthan 0.4.
 6. The system of claim 1, wherein the numerical aperture ofthe beam incident on the thin disk gain media is greater than 0.5. 7.The system of claim 1, wherein the coupler is selected from a funnel, acylindrical lens to collimate a fast axis divergence of the pump source,several cylindrical lenses, a beam shaper, a lens duct, and a beamcombiner.
 8. The system of claim 1, further comprising: a cooling devicecoupled to the cooling surface of the thin disk gain media.
 9. Thesystem of claim 1, wherein the thin disk gain media is made of astoichiometric gain material.
 10. The system of claim 1, wherein thethin disk gain media is made of a stoichiometric Yb³⁺ material.
 11. Thesystem of claim 10, wherein the stoichiometric Yb³⁺ material is YbAG.12. The system of claim 10, wherein the stoichiometric Yb³⁺ material isKYbW.
 13. The system of claim 1, wherein the thin disk gain media ismade of a semiconductor material.
 14. The system of claim 1, wherein thediode pump source is a stack of diode bars.
 15. The system of claim 1,wherein the coupler is a non-imaging concentrator.
 16. The system ofclaim 15, wherein the non-imaging concentrator is a lens duct.
 17. Thesystem of claim 1, wherein the coupler is a beam homogenizer.
 18. Thesystem of claim 15, wherein the non-imaging concentrator is configuredto convert a large beam with a low numerical aperture from the diodepump source into a smaller beam with a larger numerical aperture. 19.The system of claim 15, wherein the non-imaging concentrator reduces abeam size from the diode pump source by a factor of at least two and thenumerical aperture of the beam from the diode pump source increases byat least two.
 20. The system of claim 15, wherein the non-imagingconcentrator is a hollow funnel.
 21. An optical system, comprising: atleast first and second high power diode pump sources producing first andsecond pump beams; a thin disk gain media; a first coupler and a secondcoupler positioned between each of the diode pump sources and the thindisk gain media; and wherein the first and second pump beams areincident on the thin disk gain media from different directions.
 22. Thesystem of claim 21, wherein the optical couplers produce first andsecond beams from the first and second diode pump sources that each havea large numerical aperture incident on the thin disk gain media.
 23. Thesystem of claim 21, wherein the pump sources produce a power of at least50W.
 24. The system of claim 21, wherein the pump sources produce apower of at least 200W.
 25. The system of claim 21, wherein thenumerical aperture of each of the first and second beams incident on thethin disk gain media is greater than 0.35
 26. The system of claim 21,wherein the numerical aperture of each of the first and second beamsincident on the thin disk gain media is greater than 0.4.
 27. The systemof claim 21, wherein the numerical aperture of each of the first andsecond beams incident on the thin disk gain media is greater than 0.5.28. The system of claim 21, wherein the coupler is selected from afunnel, a cylindrical lens to collimate a fast axis divergence of thepump source, several cylindrical lenses, a beam shaper, a lens duct, anda beam combiner.
 29. The system of claim 21, further comprising: acooling device coupled to the cooling surface of the thin disk gainmedia.
 30. The system of claim 21, wherein the thin disk gain media ismade of a stoichiometric gain material.
 31. The system of claim 21,wherein the thin disk gain media is made of a stoichiometric Yb³⁺material.
 32. The system of claim 31, wherein the stoichiometric Yb³⁺material is YbAG.
 33. The system of claim 31, wherein the stoichiometricYb³⁺ material is KYbW.
 34. The system of claim 21, wherein the thin diskgain media is made of a semiconductor material.
 35. The system of claim21, wherein the diode pump source is a stack of diode bars.
 36. Thesystem of claim 21, wherein the coupler is a non-imaging concentrator.37. The system of claim 36, wherein the non-imaging concentrator is alens duct.
 38. The system of claim 21, wherein the coupler is a beamhomogenizer.
 39. The system of claim 36, wherein the non-imagingconcentrator is configured to convert a large beam with a low numericalaperture from the diode pump source into a smaller beam with a largernumerical aperture.
 40. The system of claim 36, wherein the non-imagingconcentrator reduces a beam size from the diode pump source by a factorof at least two and the numerical aperture of the beam from the diodepump source increases by at least two.
 41. The system of claim 36,wherein the non-imaging concentrator is a hollow funnel.
 42. A method ofpumping a thin disk gain media, comprising: producing a high power diodepump beam from a pump source; passing the high power diode pump beamthrough an optical coupler positioned between the diode pump source anda thin disk gain media; forming a high numerical aperture output beamfrom the optical coupler; and positioning the high numerical apertureoutput beam at an incidence surface of the thin disk gain media.
 43. Themethod of claim 42, wherein the pump beam has a power of at least 50W.44. The method of claim 42, wherein the pump beam has a power of atleast 200W.
 45. The method of claim 42, wherein the numerical apertureof the beam incident on the thin disk gain media is greater than 0.35.46. The method of claim 42, wherein the numerical aperture of the highnumerical output beam is greater than 0.4.
 47. The method of claim 42,wherein the numerical aperture of the high numerical output beam isgreater than 0.5.
 48. The method of claim 42, wherein the opticalcoupler is selected from a funnel, a cylindrical lens to collimate afast axis divergence of the pump source, several cylindrical lenses, abeam shaper, a lens duct, and a beam combiner.
 49. The method of claim42, further comprising: cooling a cooling surface of the thin disk gainmedia.
 50. The method of claim 42, wherein the thin disk gain media ismade of a stoichiometric gain material.
 51. The method of claim 42,wherein the thin disk gain media is made of a stoichiometric Yb³⁺material.
 52. The method of claim 51, wherein the stoichiometric Yb³⁺material is YbAG.
 53. The method of claim 51, wherein the stoichiometricYb³⁺ material is KYbW.
 54. The system of claim 52, wherein the thin diskgain media is made of a semiconductor material.
 55. The method of claim42, wherein the diode pump source is a stack of diode bars.
 56. A methodof materials processing, comprising: producing a high power diode pumpbeam from a pump source; passing the high power diode pump beam throughan optical coupler positioned between the diode pump source and a thindisk gain media; creating a high numerical aperture output beam from theoptical coupler; positioning the high numerical aperture output beam atthe incidence surface of the thin disk gain media to produce an outputbeam; and directing the output beam to an article to be processed.
 57. Amethod of pumping a thin disk gain media, comprising: producing firstand second pump beams from first and second pump sources; passing thefirst and second pump beams through a first and second optical couplerpositioned between each diode pump source and a thin disk gain media toproduce first and second pump beams positioning the first and secondpump beams on the thin disk gain media from different directions. 58.The method of claim 57, wherein the first and second pump beams each arehigh numerical aperture beams.